DESCRIPTION(Verbatim from the Applicant's Abstract): This NIH R01 application is an integral part of the applicant's ongoing research program focused on how the diverse types of neurons found in the mammalian nervous system are generated and maintained throughout life. This application is the competing continuation of NIH award R01-HD33442. We are currently studying DNA-binding factors that serve as transcriptional regulators in the developing and mature nervous system, specifically the POU-domain factor Brn-3.0 and related molecules. The expression pattern of Brn-3.0, described in our previous work, indicates a role in the terminal differentiation and maintenance of specific neurons in the CNS and peripheral sensory system. We have shown that the initial pattern of Brn-3.0 expression in the dorsal neural tube is negatively regulated by the ventral signal SHH. Brn-3.0 characterizes specific neurons throughout life, due in part to recently identified autoregulatory elements in brn-3.0 genomic locus through which Brn3.0 can strongly enhance its own transcription. Targeted disruption of Brn-3.0 in mice results in neonatal death and loss of neurons in the sensory ganglia and some CNS nuclei which express this factor. One model for this neuronal loss is a failure of Brn-3.0(-/-) neurons to respond to neurotrophins which are necessary for survival. However, it is not known whether neonatal death is due to loss of the central or peripheral functions of Brn-3.0, or both. The Specific Aims of this application are: 1) Further define the independent enhancer regions that target Brn-3.0 expression to the sensory peripheral nervous system and specific CNS neurons. 2) Use mice expressing marker genes under control of the Brn-3.0 sensory enhancer to examine neuronal development in mice deficient in key regulators of neurodevelopment, including Brn-3.0 itself and selected neurotrophins and their receptors. 3) Examine the molecular mechanisms of the regulation of PNS- and CNS-specific expression of Brn-3.0. 4) Target expression of an axonal marker, tau-beta-gal, to Brn-3.0 neurons by homologous recombination at the Brn-3.0 locus (partially complete under R03-MH58447). 5) Distinguish the roles of Brn-3.0 in the sensory peripheral nervous system and CNS by partially rescuing the Brn-3.0 null phenotype in the sensory system via expression of Brn-3.0 under its sensory-specific enhancer. Together these aims will make a substantial contribution to understanding the basic mechanisms of neuronal development and advance our knowledge of the many neurological and behavioral illnesses which have a genetic or developmental component.